The growing number of people who have the disease is troubling, because there are only four approved drugs that treat symptoms of the disease, and several hopeful treatments have failed key studies in 2017.

Unexpectedly, it's something researchers at the top cancer hospital in the US are looking into. While cancer and Alzheimer's seemingly don't have that much in common, there is one key link that researchers at MD Anderson think could be useful: People with a history of cancer are less likely to get Alzheimer's, while people with Alzheimer's are less likely to get cancer.

"Age is the biggest risk factor for both. But then for some reason, some people go one direction, others go another direction," Jim Ray, head of research for the Neurodegeneration Consortium at MD Anderson told Business Insider.

In the last decade the researchers have made this observational link between the development of Alzheimer's and a decreased cancer risk and vice versa. So researchers have been hypothesizing why that happens. At a very simplified level, the cause of the diseases might hold the biggest clue. "Cancer is a disease of cells that cannot die, will not die. Alzheimer's is a disease of cells that are supposed to live your entire lifetime that you can't keep alive," he said.

One of the ways researchers have been getting clues into the link is in cancer patients who have chemotherapy-related cognitive dysfunction. An estimated 75% of cancer patients have some level of cognitive impairment (memory loss, attention problems, etc.). Chemotherapy works by killing cancer cells by targeting fast-dividing cells, and in most cases, kills off some healthy cells along the way, including nerve cells in the brain.

"It's an understudied area," Ray said. "And I think a lot of people didn't fully realize it was a problem."

It's something drug researchers have started looking into, to see if there could be a therapy that prevents the neurological damage that happens with chemotherapy. If they can figure out what's going on and how to prevent the neurological side effects for cancer patients, the same approach could hold some promise in treating Alzheimer's as well.

Why cancer researchers are looking for new ways to tackle Alzheimer's

The search for new Alzheimer's treatments hasn't been going well. The last new drug approved was back in 2003, and a slew of failed trials in the beginning of 2017 has cast a shadow over the field.

Still, more drugs are in late-stage trials that could have an impact on the disease, and researchers are pinning hopes on diagnosing the disease early, before symptoms even show up. If any of those treatments pan out, it could change the way we look at the disease and potentially make the statistics a lot less dire.

Unlike some of the promising treatments that have failed in 2017 that deal with the so-called "amyloid hypothesis" (the treatments target amyloid beta deposits in the brain that accumulate in people with Alzheimer's disease), approaches that try to prevent nerve cells from dying wouldn't have any impact on that buildup. Instead of trying to clear the body of the deposits, it would just try to strengthen the nerve cells that are there.

"What we're trying to do is make your nerve cells more resistant to damage," Ray said. "It won't stop the damage, but it'd just make them more resistant longer, be more resilient."